Preparation of mercurial printing surfaces



ATN

ARTHUR vRONALD TRIST, 0F LONDON, ENGLAND.

PREPARATION OF MERCURIAL PRINTING SURFACES Application filed September 8, 1924, Serial No. 736,627, and in Great Britain September 10, 1923.

This invention relates to improvements in the preparation of mercurial printing surfaces and has `for its object the p rovision of means 4whereby a much longer printing life and more regular and controllable operation is obtained than has been possible heretofore.

When dealing' with mercurial printing surfaces, that is to say, surfaces comprising 4 mercurial or mercurized ink repelling areas and ink retaining areas much difficulty has been experienced owing to the undesirable diffusion of the mercury throughout the printing plate and also in the readiness with which the mercurized'surfaces asher'etofore produced lhave been destroyed.

Experiments have shown that with a mercurial printingr surface if all'4 t-lie parts are planographic in the real sense of the word then La very long printing life is obtained provided that the mercurized metal of which the inkrepell-ing areas are formed is wholly supported and maintained in position by a metal unaected by mercury.

The present invention consists in the formation ofa printing surface of the type specified in which the mercurized metal of which each ink repelling areaI is formed is wholly supported and maintained in place by a metal unaffected -by mercury and suitable for forming the ink retaining areas, means being provided to 'cause the mercurized metal to adherel to and/or interlock with the said metal.

In the drawings :A

Figure 1 illustrates the first step in producing a printing plate according to this invention.

Figure 2 illustrates the same part of the same plate illustrated in Figure 1 after the bichromated fish glue image has been applied thereto and'baked.

Figure 3 illustrates the same part of the I same plate after etching.

Figure 4 illustrates the same part of the same plate after the first electrodeposit.

Figure 5 illustrates the same part of the same plate after repeated electrodeposits of v,different metals have been effected.

rFigure 6 is an enlarged cross section showing therepeated electrodeposits 'more clearly.

Figure 7 illustrates the same part of the same plate as illustrated in Figures 1 to 5 inclusive after the burnt enamel has been removed.

Figure 8 shows the finished surface.

The upper surface Z7 of the nickel layer b is coated with bichromated fish glue enamel and a photo print is taken from a suitable nega-tive transparency preferably by means of a point source of light. After exposure7 the print is wash developed and baked in well known'I manner.` The result of these manipulations is illustrated in Figure 2 in which the parts c represent the baked dots of the image.

'lfhe surface b with the baked enamel parts o is now treated with a suitable mordant, for example perchloride of iron, to etch away the exposed parts of the surface b until the thickness of the layer b has been locally reduced from one thousandth of an inch in thickness to between five and six ten thousandths of an inch in thickness thus producing elevations b2 beneath the parts c.

Obviously the dimensions may be varied in practice to obtain a longer printing life for the finished surface.

When the desired degree of treatment has been effected the plate is washed and a veryv thin layer d of copper is electrically deposited on the exposed parts as illustrated in Figure 4. Experience has shown that it is ver .difficult to satisfactorily electrically deposlt any other metal on to nickel which r can be readily amalgamated by mercury other than copper andv` for this reason therstdeposit is of that metal.

Upon the layer d ofcopper a very thin layer e of silver is electrically deposited and on the layer e a second very thin layer d of-copper is electrically deposited and so on,

so that eventually the parts removed by etch-- ing are more or less filled up with the layers d, e, al', e', d2, e2, of copper and silver altennatdely deposited as illustrated in Figures 5 an 6. -i

The baked bichromated fish glue enamel parts c are now removed by means of a suitable alkali, such for example as a solution of cyanide of potassium or cyanide of sodium.

It is essential to the invention that the metal deposited after the treatment by the mordant or etch shall produce the ink repelling areas as when such deposit is efiected and the parts c are removed by alkali treatment a slight upstanding ridge f is formed about each individual elevation b2 as illustrated in Figures 6 and 7.

The surface of the plate is now treated with metallic mercury with the result that the deposits d, e, d', e, cl3-2,162, and the upstanding ridges f are quickly amalgamated producing mercurized ink repelling areas g, which are (if so desired) truly planographic with respect to the ink retaining areas.

From the above it Will be seen that the ink repelling area g is supported by the nickel layer l; which is unaffected by mercury and that the area g is Wholly retained in place by a fioor and Walls integrally associated therewith so that the area g forms an isolated pool of mercurized metal Wholly supported by nickel which is unaected by mercury. l

In some cases the silver layers e, e', e2, may be replaced by gold layers and after the initial layer d of copper has been deposited a composite deposition of copper and silver or copper and gold may beernployed in place of the layers e, d', e, d2, e2, Without departing from the invention.

Although in describing the invention for the purpose of example, reference has been made to the use of an iron .plate having an electrodeposit of nickel 'obviously a nickel plat-e may be employed or the nickel layer may be applied to any suitable substance or material in any known Way that may be convenient; similarly the bichromated fish glue enamel may be replaced by any light sensitive medium which will after exposure and treatment provide an adequate resist.

1. A planographic printing plate comprising a layer of metal which is unaffected by mercury and which is suitable for forming ink retaining areas, recesses in said layer of metal arranged to leave the printing areas as projections and a mercurized .metal filling located in said recesses and firmly adherent to said recesses, said mercurized metal filling producing the nonprinting areas.

2. A planographic printing plate comprising a layer of metal which is unaffected by mercury and which is suitable for forming ink retaining areas, recesses-in said layer of metal arrangedto leave projecting printing areas; a metallic coating in each recess, said coating being of a metal which will adhere to the surface of the recess and to which mercury will adhere; and a mercurized metal filling located in said coated recesses and firmly adherent. to said recesses, said mercurized metal filling producing the nonprinting areas.

3. A planographic printing plate comprising a layer of nickel; recesses in said nickel layer arranged to leave projecting printing areas; a copper coating in each recess;

.alternate silver and copper layers in each recess; and mercury in each recess for producing mercurized metal nonprinting areas disposed in the plane containing the printing areas.

ll. A process for producing a planographic printing plate comprising the local application of a resist to a nickel layer, etching the exposed parts of the nickel sheet by a mordant to locally reduce the thickness of the nickel layer and produce recesses, electrodepositing a very thin layer of copper on the etched parts of the nickel sheet, electrodeposit-ing alternately verythin layers of silver and copper on the copper layer, removing the resist and applying mercury to the surface of the plate so that the copper and silver layersmay be amalgamated to produce ink repelling areas. l

5. A process for producing a planographic printing plate comprising the application of light sensitive bichromated fish glue to one surface of a nickel layer, exposing said fish glue to light through a negative transparency, Wash development of the image to remove the unexpos'ed parts of the fish glue, treatment of the plate by heat to bake the exposed fish glue to form local resists on the nickel layer, etching the parts of the nickel layer not protected by the resist With a mordant to locally reduce the thickness of the nickel layer and produce recesses,

electrodepositing a very thin layer of' copper .l name to this specification.

ARTHUR RONALD TRIST. 

